1.5T Calling all turbo freaks and Tuners: TURBO FLUTTER UNDER ACCELERATION

[kidcon]

https://datazap.me/u/kidcon/log-1535592772?log=0&data=1

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[KTuner]

So recently I have been noticing when I am accelerating my turbo stutters - I am not quite sure why.

I don't know what "turbo stutters" means. Can you offer a better description? You're hitting the targets.

Get rid of the BOV and try again.

 

[Micah]

I don't know what "turbo stutters" means. Can you offer a better description? You're hitting the targets.

Get rid of the BOV and try again.

Post #15 - he claims to have the stock BOV (which is BPV, but I digress)

 

[kidcon]

Post #15 - he claims to have the stock BOV (which is BPV, but I digress)

Yes I know it’s BPV I just put BOV because it was asked and forgot lol - but as far as the turbo sounds it’s like a really fast ftftftft instead of a steady sssssssssss sound if that makes any more sense

 

[KTuner]

Yes I know it’s BPV I just put BOV because it was asked and forgot lol - but as far as the turbo sounds it’s like a really fast ftftftft instead of a steady sssssssssss sound if that makes any more sense

Is this something you've just finally noticed or has it actually changed? Sounds like you're hearing bleed-off while the ECU is trying to maintain target boost pressure.

 

[kidcon]

Is this something you've just finally noticed or has it actually changed? Sounds like you're hearing bleed-off while the ECU is trying to maintain target boost pressure.

It is something Ive noticed more and more while driving, i first heard it about a month ago but only for a second, now it is the whole time in boost. not sure what you mean by bleed off?

 

[Micah]

Are you hearing wastegate flutter?

 

[kidcon]

Are you hearing wastegate flutter?

wouldnt wastegate flutter be when i take my foot off the gas?

 

[typemismatch]

wouldnt wastegate flutter be when i take my foot off the gas?

No, the wastegate controls how much boost the turbo makes by controlling how much exhaust is going to the turbine wheel. When the turbo is at the target boost the wastegate will open and close, potentially very fast and repeatedly, to divert exhaust away from the turbo and keep the boost pressure steady.

A free flowing exhaust (larger diameter/no cat) will help the exhaust flow over the turbine wheel faster which, in turn, raises boost pressure faster. The lower the pressure in the exhaust the faster boost will build and the more the wastegate will work to keep boost at the target pressure. This could easily be the "flutter" noise you hear.

 

[Micah]

wouldnt wastegate flutter be when i take my foot off the gas?

lol - not really. By Pass Valve or Blow Off Valve would be when you take your foot off the gas. Wastegate Flutter would be when the turbo is avoiding making more boost than desired. The wastegate is a flapper on the exhaust side of the turbo (typically internal, but can also be externally "gated") and while on most (older) turbo designs the wastegate is mechanically controlled with vacuum pressure and a spring loaded armature... on our cars it is electronically controlled.

BPV/BOV is on the intake side, usually controlled by vacuum. For more detail - see the link about BOV's in my signature.

 

[Micah]

 

[kidcon]

Ah okay, thank you both for explaining more, I get the BOV/BPV stuff just not the wastegate. So my question is now then why would my exhaust be an issue, it is larger diameter than stock and more free flowing, same with my catless DP.

I also have this issue with ECON on because I am using the Dual map. Wouldnt the lower amount of boost pressure there mean the wastegate wouldnt be opening and closing as rapidly due to the wastegate spring being used at its intended pressures? or am i still not fully understanding?

Thanks for all the help guys @KTuner @Micah @typemismatch

 

[Micah]

Totally a guess, maybe reduced backpressure from the larger exhuast and less restrictive catless downpipe is changing how the car behaves on the tune you are running. If that's the case, would be good to ensure safe values are being seen in the datalog..... and arguably you could make more power if you were to get a custom tune performed (I would recommend Derek at IMW).

I could be completely off the mark though, it might not be your exhaust at all. The best way to verify would be to swap back the stock exhaust components, first the downpipe or the exhaust, each on their own, and together. Meaning stock dp, stock exhasut//catless dp, stock exhaust//catless dp, larger exhaust(you've already got that on the car). I know this would be a major pain in the ass.... so instead I would recommend you flash the "like stock" calibration and drive around for a couple days to see how it behaves.

 

[kidcon]

Totally a guess, maybe reduced backpressure from the larger exhuast and less restrictive catless downpipe is changing how the car behaves on the tune you are running. If that's the case, would be good to ensure safe values are being seen in the datalog..... and arguably you could make more power if you were to get a custom tune performed (I would recommend Derek at IMW).

I could be completely off the mark though, it might not be your exhaust at all. The best way to verify would be to swap back the stock exhaust components, first the downpipe or the exhaust, each on their own, and together. Meaning stock dp, stock exhasut//catless dp, stock exhaust//catless dp, larger exhaust(you've already got that on the car). I know this would be a major pain in the ass.... so instead I would recommend you flash the "like stock" calibration and drive around for a couple days to see how it behaves.

Okay, im going to flash back to the "stock like" map when i get out of work tonight, I have to drive 2 hours into jersey for a wedding this weekend. I will be checking to make sure I also dont have any lose components so ill be torquing everything down and see if that helps also. I have wanted to do a custom tune but dont want to start until i get my new intake and intercooler as things will change with those. If this weekend doesnt fix the issue ill have to head to my parents in Cuse and get to swapping parts and see whats up!

Thanks again for explaining this to me, I never understood wastegates but had all the other boost shit down a lot better haha

 

[typemismatch]

Ah okay, thank you both for explaining more, I get the BOV/BPV stuff just not the wastegate. So my question is now then why would my exhaust be an issue, it is larger diameter than stock and more free flowing, same with my catless DP.

I also have this issue with ECON on because I am using the Dual map. Wouldnt the lower amount of boost pressure there mean the wastegate wouldnt be opening and closing as rapidly due to the wastegate spring being used at its intended pressures? or am i still not fully understanding?

Thanks for all the help guys @KTuner @Micah @typemismatch

Your freer flowing exhaust piping allows exhaust gases to exit the turbo faster. The faster the turbine spins, the more boost pressure is created on the compressor side. With a smaller exhaust, pressure builds up behind the turbo slowing down the exhaust gasses and how fast the turbine spins.

The turbine (the exhaust side of the turbo) is like a pinwheel. If you try blowing through a straw at a pinwheel, you can get it spinning, but it takes effort. If you blow on it through a piece of garden hose, you can get it spinning more quickly because more air can flow over it faster. A wastegate is like having a hole in the straw/hose that you can open and close to limit the air going to the pinwheel, let's say by covering the hole with your finger for example.

It's not exactly the same (backwards, but similar), but I hope that covers the basic idea in a visual way.

So why does this cause your wastegate to flutter? Freer flowing exhaust lets the turbo "spool up" faster, so the wastegate needs to work more to keep the turbo spinning at the right speed to make the boost you want.

Changing your tune probably won't affect your wastegate the way you think it will. The less boost you want to run, the more the wastegate works to bypass the turbo. So throwing a stock map on it will probably cause more "flutter" noise.

PS. I know I'm leaving out the thermodynamics, exhaust expansion, and pressure optimization stuff, but, I didn't want to add confusion.

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